Method of and apparatus for recovering spent pickling solutions



H. S. MARSH ET AL METHOD OF AND APPARATUS FOR RECOVERING SPENT PICKLINGSOLUTIONS Filed Dec. 24, 1920 4 sheets-shcet l WI TA/ESSES Apr. 3, 1923.l,45@,2i6

4 H. s MARSH ET AL METHOD OF AND APPARATUS FOR RECOVERING SPENT PICKLINGSOLUTIONS Filed Dec. 24, 1920 4 sheets-sheet 2 Apr. 3, 1923. 1,450,216

' H. S. MARSH ET AL METHOD OF AND APPARATUS FOR RECOVERING SPENTPICKLING SOLUTIONS Filed Dec. 24, 1920 4 sheets-sheet 5 F v g x /N VEN7036 WITNESSES d sa wxm Apr. 3, 1923.

H. 5. MARSH ET AL METHOD OF AND APPARATUS FOR RECOVERING SPENT PICKLINGSOLUTIONS 4 sheets-sheet 4 INVENTOR 3. W 5. 508% Filed Dec. 24,

Patented Apr. 3, 1923.

UNITED STATES ion-m.

HENRY s. MARSH AND BALI s. cocnnau, or y'otmcs'rown, omo.

METHOD OF AND APPARATUS FOR BECOVERING SPENT PICKLING SOLUTIONS.

' Application filed December 24, 1920. Serial No. 432,852.

To all whom it may concern Be it known that we, HENRY S. MARSH and RALFS. COCHRAN, residing at Youngstown, in the-county of Mahoning and Stateof Ohio, both'citizens of the United States,

,have invented or discovered certain new and useful Improvements inMethod of and Apparatus for Recovering Spent Pickling Solutions, ofwhich improvements the following is a specification.

Our invention relates to the recovery of spent pickling solutions,solutions initially acid and which through continued use have becomeheavily laden with salts in solution.

Such are the exhausted and enfeebled solutions which come from thepickling vats of steel mills. Our present invention consists inimprovements upon the method and apparatus set forth and described 1nour application for United States Letters Patent,

Serial No. 350,383, filed January 9, 1920,

and allowed October 18, 1920. The invention, primarily intended for thepurpose stated, is of wider applicability, as eventually will appear.

Our invention is illustrated in the accompanying drawings. Fig. I is aplan view .from above of reclaiming apparatus in the construction andoperation of WhlCh our present improvements in apparatus and in methodare realized; Fig. II is a v1ew in vertical longitudinal section, on theplane indicated by the line II--II, Fig. I; Fig.-

lustrating the handling of the salt when removed from. theprecipitationchamber; Fig. VII is a diagrammatic view in plan of the layout of thewhole.

Referring to Fig. I, we provide two troughs 1 and 2 of heat-insulatingmaterial resistant to acid attack. Conveniently these troughs are madeof wood. They are arranged in series, to receive and convey. anadvancing stream ofpickling solution; a

\ supply pipe 3 enters'trough 1 at one end; a

connecting pipe 4 leads from trough 1, at

the end remote from the entry of pipe 3 (the 'may'come directly from thepic down-stream end), to one end of trough 2; from the farther end oftrough 2 a delivery pipe 5 leads. The intake throu h pipe 3 ling vat, orit may come from a storage tank. Fig. VII shows a storage tank 6 ofparticular structure. The spent acid from the pickling tanks, elevatedif need be by suitable means, such as an air lift, flows through asupply pipe 7 and enters tank 6 through a screen 8. The space within thetank, between inlet and outlet is divided by a series of bafilepartitions 9, so arranged as to cause the solution to advance throughthe tank in a succession of vertical, alternately rising and descendingreaches. An arrangement of partitions such as to effect this end' willpresently be explained in describing trough 1, and further descriptionon this {point will be deferred. The contents of the tank 75 (initiallyhot) may or may not be heated additionally. Heating means are wellknown, and in our earlier application already alluded to we haveindicated such means. The reason for so screening the-flow of picklingsolution and then driving it in circuitous course is to separate dirt-toseparate by deposit such heavy substance-as scale and to. remove byskimming such light substanceas sawdust. The purpose isthat, if therecovered salt is to be used commercially, such substances as mightotherwise accumulate with the salt and adulterate it, will be removedbefore the solution leaves tank 90 6. If the recovered salt is to bewasted, or if it is to be used in such manner that contamination isunimportant, such special means for cleaning need not be employed.Returning now to particular description of trough 1, its internalconstruction will be understoodon comparing Figs. I and III. It' is 'along, deep trough the space within is divided by transverse partitionsso proportioned and arranged as to cause the 100 advancing stream toflow up and down through a succession of vertically arrangedpassageways. The partitions stand alternately at different heights; thesuccession of partitions 10 stand free of the bottom of the tank andsomewhat above the level of the flowing stream. The alternate partitions11 rise from the bottom of the tank I and do not reach the surface ofthe fiowin stream. This arrangement of partitionswil l i be clearlyunderstood from a glance at Fig.

II, which is ashas been said, a section through trough 2 and in whichthe partitions 20 and 21 are arranged substantially as partitions 10 and11 are arranged in trough 1. The level of the upper edges of partitions11 in trough l and 21 in trough 2 is, in Figure III, indicated by theline 01b; the level of the partitions 10 and 20 is indicated by the line0d; the level of the lower edges of partitions 10 and 20 is indicated bythe line e-f. Of the level of the lower edges of partitions 21, moreremains to be said, when we come to describe trough 2.

It ma now properly be remarked that the partitions 9 in tank 6 arearranged in substantially the same manner, to effect the same verticalcircuitous flow.

The progress of the flow of the solution through trough 1 will be downfrom intake 3, beneath the first partition 10, up and over the firstartit-ion 11, then down again; circuitous ow continues until at lengththe stream, rising beyond the last partition 10 escapes through the pipe4.

Into the passageways formed for the flowing stream by and between thesepartitions 10 and 11into some or all of them, as may be found expedient,depend coils 12, such as are particularly illustrated in Figs. IV and V,of a circulation pipe, presently to be more particularly described andcharacterized. Sufiice it here to say that these coils are formed ofheat-conducting material, (convenient-l of copper) and the structure inthis detail is essentially a. heat-exchanger. Manifestly, the particularform of coil illustrated in Figs. IV and V is exemplary. Such particulararrangement within the knowledge of the engineer, will be resorted to ashe may prefer, to provide the essential extended heat-exchanging walls.

In the bottom of trough 1 and extending longitudinally throughout itsextent, or throughout so much of its extent at least as is occupied bythe heat-exchanging apparatus indicated, lie pipes 14, perforated atintervals and carrying under pressure a suitable gasconveniently air-tobubble through the stream as it flows. The function of such inblown gasis to agitate the flowing stream of solution, and to intensify andquicken the heat-excha-n ing action.

Comin now to troug 2, it is in general features 'ke trough 1. Fig. IIIshows it to be deeper than trough 1. and to be hopper shaped at thebottom. Partitions 21 are at their lower ends so shaped and positionedas to afford a continuous space in the bottom of the trough, in whichspace the preci itated salt 00 lects, and from which the co leoted saltmay by suitable means be withdrawn; for example, by the spiral conveyor23,

It is desirable to agitate the stream in trough 2, as well as introughl, and that by like means. The accumulating of precipitate intrough 2 and the removal of the accumulation render it undesirable toarrange pipes for injection of gas along the bottom of trough 2;instead, pipes 24 extend above tank 2, and these are provided withdepending branches, and these extend-down to approximately the bottom oftrough 2 and there they discharge their jets of inblown gas.

In the passageways of trough 2, as in those of trough 1, coils of pipeare arranged, to serve as heat-exchanging members. The solution as itfiows from trough 2 through conduit 5 returns upon itself, and traversesin turn certain of the coils arranged in the passageways of trough 2(those designated 22) and then the coils 12 in the passageways oftrough 1. The direction of flow of this return branch of the loopedstream is countercurrent to the branch advancing through the passagewaysand inundating the coils. Fig. I diagrammatically shows three coils ineach passageway. The number may be varied. From the coils 12 in tank 1the now reclaimed solution flows through pipe 34 to storage tank 30, or,it may be, directly to the pickling vats.

e have just remarked that the return branch of the looped streamtraverses cermm of the coils arranged in the passageways of trough 2.The drawings (Fig. I) show the trough subdivided by the partitions 20,21, into twelve passageways; in all of these passageways, excepting thelast two (last relatively to the right-to-left flow. of the advancingstream) coils are shown to be placed. Through the coils of the firstfive passageways the return branch of the stream advances, from left toright, countercurrent to the incoming stream. It now appears that thestream as it flows through the apparatus flows in loop form, thebranches of the loop in heat-transferring relation, one to the other.The loop, a phrase which we shall hereafter employ, designates thecourse of the stream. from its advance beyond passageway A, Fig. 1', toits return to the point B where it is about to 'enter the first of the.coils 22.

In our earlier application mentioned above we describe apparatus inwhich the flowing stream is looped to effect the same ends as thosehere-contemplated. The flow of the liquid under treatment is theremaintained by gravity. With refinement and elaboration of apparatus wefind it desirable to pump the liquid through the return branch of thecircuit; and to that end we show in Fig. I a pump 31, arranged inconduit 5 between the pointof emergence from trough 2 and the pointwhere the stream enters the first of the coils 22.

We have said that the first five of the twelve passageways of trough 2contain coils 22. It will be observed that of the remaining sevenpassageways, the first five contain similar coils 5;v and it will beobserved further that nozzles for blowing in agitating gas enter all ofthe passageways of trough 2, excepting the last. This last passageway isfree bothof heat-exchanging coils and of gas nozzles; the nextpassagewayto the last, though it contains gas nozzles, is free ofheat-exchanging coils.

The coils 25 in the five intermediate passageways of trough 2 are partof a refrigeration unit; through them courses a suitable cooling fluid-it may be brine, it may be ammonia, it may be other fluid, depending onthe particular nature of the refrigeration unit chosen. Many sorts ofrefrigeration apparatus are known, and the engineer may exercise hisjudgment or preference in selecting one or the other. The flow of coolinfluid through the bank of coils 25 is pre erably from left toright,'Fig. I- countercurrent to the right-to-left advance of theincoming stream through trough 2.

The number of passageways into which the troughs are subdivided is notimportent-indeed, the provision of a plurality of troughs is, in thebroader .aspect of the problem, a matter of convenience in assembly andarrangement of 'component pieces of apparatus. But (with the arrangementof trough 2 as shown'in Fig. I particularly in view), the essentialfeatures are that the advancing incoming stream shall wash, first,

the heat-exchanging coils 22 in which the return stream flows, that itshall then wash, second, the coils 25 in which the cooling agent flows,and that it shall then flow through a further portion of trough 2 freeof heat-exchanging coils. It is further desirable that agitation of theadvancing stream maintained Where the stream'washes coils-22 and 25,shall continue in that portion of the trough 2 which. is free of coils,but shall not continue tothe end of trough 2.

It will in some cases be found that because of depletion in volume thereturn stream will not beadequate to afford the preliminary coolingdesired. In such case supplemental cooling means maybe resorted to. Forexample certain of the coils 12in trough 1 may be taken out of the lineof circulation of' the returning stream of reclaimed solution, andthrough them cold water (or other cooling fluid) may be circulated.

Again, because of'diminution of volume I of liquid, consequent uponcrystallization of the salt (ordinarily copperas, carrying 45% water ofcrystallization), the reclaimed solution may be of too great strength,as regards its acid content. In such case an additional supply of watermay be introduced.

The feed p'pe 15, through which liquid recovered in centrifu e 28 may bereturned, is a suitable pi e or the introduction of additional supp iesofwater also. If the ,water so introduced be cold, it may in virtue ofthat characteristic correct the difliculty (if such difficulty exists)just mentioned, of too little cooling effect of the outgoing liquid uponthe incoming.

Note has been made above of the fact that the precipitated salt isremoved from the bottom of trou gh 2 by means of a spiral conveyor 23. Ihis conveyor, be itvnoted, is arranged to remove the salt in aleft-toright direction, moving it fromthe cooler to the warmer end ofthe trough. Such is the preferred, though not the necessary,arrangement. At the right-hand end of trough 2 conveyor 23 delivers thesalt to a sump 26, whence it is raised by a second spiral conveyor,arranged in an inclined spout 27, to a level higher than the surface ofliquid in troughs 1 and 2. From spout 27 the slush of crystals and acidpasses in continuous feed to a tank 40, and thence in successivechargesto a centrifuge 28. From the centrifuge the liquid returns,impelled if need be by an air lift or equivalent apparatus,.and reentersthe stream flowing in the reclaiming apparatus. This reentry may be atany desired point. For example, it may enter the trough 2, through pipe33.

In a small installation it may be desirable to unite the two tanks endto end, making a single tank (as obviously may be done). In such case,the removal of crys-- tals would preferably be from an intermediatepoint in the length of the trough, and the particular kind of conveyorwould be that which the engineer prefers. Y

The salt relieved of the greater part of the accompanying liquid, butstill damp, descends from the centrifuge to a vibratory, slightlyinclined, somewhat roughened, and preferably somewhat heated conveyorplatform 29. The means of heatingmay be such as the engineer prefers.Advantageously also the salt spread upon conveyor 29 may be blown uponby a suitably placed fan. ysuch means the salt is thoroughly dried, andfrom the conveyor the dried salt passes to suitable storage binorreceptacle for shipment. Instead of such a platform conveyor as thedrawings show and as the fore oing sentences characterize, we may emp oya steam-jacketed drying and mixing conveyor, of the sort now on themarket and known to engineers.

Recurring to the course of the liquid flowing from trough 2, an overflowpipe 32 is provided, leading directly from trough 2 .to

tank 30. In case of trouble with the pump, the liquid will thus be caredfor.

The operation of the apparatus now described, in which operation ourimproved through conduit 3, enters tank &

method is practiced, may be briefly indicated. The solution to betreated, flowing 1; following the circuitous vertical course described,it passes through tank 1, and, flowing thence through conduit 4, itenters tank 2 andtraverses it in like course. Emerging from tank 2, itflows through conduit 5, back through coils 22 in trough 2,-and thenthrough coils 12 in trough 1, and on to a suitable place of storage orconsumption. \Vithin trough 2 and beyond the bank of coils 22, theadvancing stream encounters first the bank of coils 25. passageway wherethe blowing with air which has attended its advance thus far through thetroughs is continued, but Where no further cooling is exercised upon it,and then before it passes from trough 2 it traverses a passageway inwhich it is neither cooled nor agitated.

The liquid under treatment enters trough 1 at high temperature, not farbelow the boiling point. The refrigerating apparatus (coils 25) is suchas to reduce the temperature of the liquid under treatment to orslightly below the freezing point of water (0 C.). But on the way frominlet to refrigerator the advancing stream comes into heat-exchangingrelation with the return stream passing from the refrigerator. Theliquid of this stream is reclaimed solution, and it at the beginning ofthe return flow is cold (the temperature is near freezing).Volumetrically the return stream is less than the entering stream,because of the removal of the salt (carrying from the liquid, be itremembered, relatively large quantities of water of crystallization). Byvirtue of the heat. exchange, the entering solution on reaching therefrigerator has already been cooled to a relatively low degree 10 C.,or thereabouts), and, accordingly, less refrigeration is required; whilethe reclaimed solution passes from the apparatus heated to a degreeapproximating that required in the pickling vat, to which it maydirectly pass.

Proportions are such that the entering solution is in trough 1 cooled toa point near but not beyond that of salt precipitation (2143 C). Intrough 2 temperature is reduced to a point somewhat below the freezingpoint of water, and substantially to the freezing point of thesolution-which is a few degrees below 0 C. Agitation of the stream as itflows expedites heat transfer and keeps the heat-transfer surface cleanof salt-crystals, and, furthermore, agitation is effective to preventformation upon the surfaces of coils 25 of ice crystals; for, if theliquid be relatively undisturbed, the water will, when a temperaturebelow zero is reached, tend so to separate and crystallize.

Precipitation begins soon after the incom- It then enters a ing solutionenters trough 2 and progresses as temperature falls. The inblown air hasthis further effect, in addition to those noted a e have been particularto describe provision such that the liquid under treatment, aftercomplete refrigeration passes on through a assageway where still it isagitated by in lown gas, and then ultimately enters a passageway whereit is no longer so agitated. Agitation prolonged beyond cooling iseffective to complete precipitation; ultimate freedom from agitationallows the precipitate to settle, and permits the drawing off throughconduiti5 of clear reclaimed liquid. I

We have been careful to explain that the precipitate is preferablycarried toward and ultimately delivered from the warmer end of trough 2.Of course in carrying crystals from cooler to warmer portions of the bodof liquid, some portion will be redissolve But the quantity soredissolved will be inconsiderable, andthere will be a more thancountervailing gain, in the cooling effect that the body of precipitatewill exert on the portions of the liquid toward the warmer end of thetrough.

We have now described the invention in its application to the specificproblem of reclaiming spent pickling solution. As we intimated at thebeginning and as now is manifest, the invention is applicable tosolutions generally, and will be found advantageous, wherever thedesirability appears of obtaining precipitation with a minimum loss ofheat.

We claim:

1. The method herein described of reclaiming spent pickling solution,which consists in causing the solution to flow in a looped circuit, thereturn branch of the circuit confined within heat-conducting walls beingsubmerged in the outgoing branch, and cooling the stream in the loop ofthe circuit.

2. The method herein described of reclaiming spent pickling solution,which consists in causing the solution to flow in a looped circuit, thebranches of the circuit in heat-transferring relation one to the other,causing the stream to submerge a heat-absorbing body arranged in theloopof the circuit, and agitating the stream of solution where it sweepsacross the heat-absorbing body.

3. The method herein described of reclaiming spent pickling solution,which consists in causing the solution to flow in a looped circuit, thebranches of the circuit in heat-transferring relation one to the other,causing the stream to submerge a heat-absorbing body arranged in theloop 1 rise through the stream of solution in the region where it sweepsacross the heat-absorLin body.

4. he method herein described of reclaiming spent pickling solution,which consists in causing the solution to flow countercurrent in loopform, the branches of the circuit in heat-exchanging relation .one tothe other, cooling the flowing stream throughout a portion of the loop,and collecting precipitate from the flowing stream throdughout theregion of cooling and beon 1 y 5. The method herein described of reclaiming spent pickling solution, which consists in causing the solutionto flow countercurrent in'loop form, the branches of the circuit inheat-exchanging relation one to the other, cooling the flowing stream inthe loop, gathering precipitate from the loop,

separating from the precipitate gathered! its accompanying liquid, andreintroducing to the circuit the liquid so separated.

6. The method herein described of reclaiming spent pickling solution,which consists in causing the solution to flow countercurrent in loopform, the. branches of the circuit in heat-exchanging relation one tothe other, cooling the flowing stream in the loop, gathering precipitatefrom the loop,

separating from the precipitate gathened its accompanying liquid, andreintroducing to the stream in the incoming branch of the circuit theliquid so separated.

7. The method herein described of reclaiming spent pickling solution,which consists in causing a stream of solution to flow countercurrent inloop form, the branches of the circuit in heat-transferring relation oneto the other, cooling the flowing stream and precipitating the salt inthe loop, and introducing an added stream of solvent into the incomingbranch of the circuit.

8. In the operation of reclaiming spent pickling solution, the stepherein described of effecting heat exchange which consists in causing acolder stream to flow in a conduit of heat-conducting material arrangedwithin a vertically flowing warmer stream, and in causing a gas tobubble through the stream last named from a point beneath such conduit.

9. The method herein described of re-' claiming spent pickling solutionwhich consists in causing the solution to flow in devious course througha succession of vertically disposed risin and descending reaches,cooling the so ution after it has traversed said reaches andprecipitating thereby its burden of salt, andthen causing the unburdenedstream to return through a conduit of heat-conductingmaterial extendingwithin said reaches.

10. The method herein described of reclaiming spent pickling solutionwhich consists in bringing the solution intocontact with aheat-absorbing body and, as the temperature falls below the freezingpoint of the solvent, causing bubbles of gas to ascend through theliquid and across the sur= face of the heat-absorbing body.

11. The method herein described of reclaiming spent pickling solutionwhich consists in causing a stream of the solution to sweep across thesurface of a heat-absorbing body and, as the temperature falls below thefreezing point of the solvent, agitating the stream.

12. The method. herein described of reclaiming spent pickling solutionwhich consists in efi'ecting precipitation by causing the solution undertreatment to flow in a stream over a cooling surface, and withdrawingthe precipitate through the stream in a direction opposite to its flow.

13. In apparatus for reclaiming spent pickling solution, means forcausing the solution to flow in a loop-formed stream with the branchesof the circuit in heat-trans- -ferring relation one to the other, saidmeans thereof, and means for agitating the stream of solution where itsweeps across such heatabsorbing body, substantially as described. i 15.In apparatus for reclaiming spent pickling solution, means for causingthe solution to flow in a loop-formed stream, with the branches of thecircuit in heat-transferring relation one to the other, a heat-absorbing body arranged to be submerged by the flowing stream in the loopthereof, and means for injecting gas into the flowing stream at a pointbeneath such cooling body, substantially as described.

16. In apparatus for reclaiming spent pickling solution, means forcausing the solution to flow in a loop-formed stream, the return branchof the stream traversing a heat-conducting-walled conduit submerged in avertically flowing reach of said stream, and means for injecting gasinto the stream at .a point beneath said conduit, substantially asdescribed. I

17. In apparatus for reclaiming spent pickling solution, a heatexchanging unit consisting of a vertically disposed passageway forliquid, a conduit disposed in said passageway, and means for injectingan agitating gas into the stream flowing in said passageway at a pointbeneath said conduit, substantially as described.

18. In apparatus for reclaiming spent pickling'solution, means forcausing the soution to flow in loop form, the branches of the circuit inheat-exchanging relation one to the other, a conduit withheat-conducting pickling solution, means for causing a stream ofsolution to flow countercurrent in circuit form, thebranches of thecircuit in heat-exchanging relation, one to the other, means for coolinga portion of the loop, and a device arranged at a point in the line offlow beyond the region of cooling for removing precipitate from theapparatus.

20. In apparatus for the reclaiming of spent pickling solution thecombination of a conductor for a stream of solution under treatment,means for effecting precipitation of salt from the stream, such meansconsisting of a cooling element arranged within the conductor andadapted to be submerged in the flowing stream, and means for withdrawingfrom the conductor, and in a direction from the cooler to the warmer endthereof, the precipitated salt, substantially as described.

21. In apparatus for recovering spent pickling solution, means forcausing the solution to flow in a looped stream, the

branches of the circuit in heat-communicating relation one to the other,means for .cooling the stream as it flows through the loop, means forgathering precipitate from.

the stream in the loop, means for separating from the precipitate sogathered its accompanying liquid, and means for returning to the flowingstream the liquid so separated, substantially as described.

22. In apparatus for the recovery of spent pickling solution thecombination of a passageway, means for precipitating salt in finelydivided form from a solution flowing in said passageway, means forremoving the precipitated salt from said passageway, and means forseparating from the precipitate so removed and for returning to thepassageway mother liquor removed with said precipitate, substantially asdescribed.

23. In apparatus for reclaiming spent pickling solution, means forcausing the solution to flow in devious course through a succession ofvertically disposed rising and descending reaches, a return conduit forthe solution formed of heat-conducting material and arranged to besubmerged in the flowing stream in one of the reaches mentioned above,means for cooling the stream as it flows in the circuit so formed, andmeans for removing from the apparatus precipitate collected by gravityat the bottom of said reaches. 1

24. In apparatus for reclaiming spent pickling solution, means forcausing the solution to fiow in devious course through a succession ofthree vertically disposed rising and descending reaches, a returnconduit for the solution formed of heat conducting material and arrangedto be swept across by the stream in the first of the reaches mentioned,and means for cooling the flowing stream in the second of such reaches,substantially as described.

25. In apparatus for reclaiming spent pickling solution, means forcausing the solution to flow in devious course through a succession ofvertically disposed rising and descending reaches, means for agitatingthe stream as it flows in such reaches, excepting the last, means forcooling the flowing stream arranged in one of the reaches in whichagitation is maintained other than the last, and areturn conduit for theflowing stream formed of heat-conducting material. and arranged to beswept across by the flowing stream in one of such reaches anterior to'that in which said cooling means are arranged, substantially asdescribed.

26. In apparatus for reclaiming spent pickling solution, four verticallydisposed passageways opening below to a common receiving space forprecipitate, and arranged to carry a stream of the solution inalternately ascending and descending reaches, a conduit formed ofheat-conducting material arranged to be submerged in the stream flowingthrough the first passageway, separate means for cooling the stream asit flows through the second passageway, means for causing an agitatinggas to rise through the stream as it flows in the first second and thirdpassageways, and means for removing the precipitate from such receivingspace, substantially as described.

27. In apparatus for reclaiming spent pickling solution, a trough,transverse partitions in said trough dividing the space within anddirecting the flow of a stream of pickling solution introduced at oneend in a succession of vertically alternately rising and descendingreaches, means for cooliriiig the advancing stream, and means for eecting a heat exchange between the cooled stream flowing from the troughand the trough, substantially as described.

28. In apparatus for reclaiming spent pickling solution, a trough,transverse partitions arranged in said trough, and directing the flow ofa stream of solution flowing through the trough into a succession ofalterthitherto uncooled stream advancing in the nately rising anddescending reaches, a return conduit for the solution passing from thetrough with heat exchanging portions arranged to be swept by the streamin the earlier reaches within the trough, and coolingmeans operativeupon the stream in intermediate reaches of the trough, substantially asdescribed. p

29. In apparatus for reclaiming spent pickling solution a plurality oftroughs subdivided within into a succession of alternately ascending anddescending passageways arranged in series and forming a continuous lineof flow for the solution to be reclaimed, a conduit leading from thedischarge end of the second trough in the line of flow and provided withcoils of heat-conducting material depending into the passageways of thefirst trough, and cooling means effective upon the flowing stream as itadvances through the second trough, substantially as described.

30. In apparatus for recovering s ent pickling solution two tanksarrange in series and adapted to carry a flowing stream of solution,subdivided internally into successions of passageways through which theadvancing stream flows alternately upward and downward, a conductorleading from the discharge end of the second trough in the line of flow,and provided with coils formed of heat-conducting material dependingsome of them into passageways of the second trough adjacent the inletend thereof, and other of said coils depending into passageways in thefirst trough, a coil of heatconducting material depending into a,passageway of the second trough adjacent the discharge end thereof, andmeans for causing a cooling fluid to flow through the coil last named,substantially as described.

31. In apparatus for recovering spent pickling solution the combinationof means for causing a stream of solution under treatment to advance ina succession of vertically ascending and descending reaches, means forcooling the advancing stream below the point of precipitation, suchmeans including a conduit of heat conducting material immersed in theflowing stream and conveying the looped-back solution after it hastrav-' ersed the reaches first defined, a refrigerator element in theloop so formed, and'an-auxiliary cooling agent operative upon the streamas it app-roaches the loop and means for removing from the apparatusprecipitated salt, substantially as described.

32. In apparatus for recovering spent pickling solution, the combinationof means for precipitating, removing, and draining the salt, and amaterial-agitating conveyor maintained at elevated temperature leadingto the point of delivery, substantially as do scribed.

33. In apparatus. for recovering spent pickling solution, thecombination of means for precipitating, removing, and draining the salt,a material-agitating conveyor maintained at elevated temperature,leading to .the point of'delivery, and means for maintaining acirculation of air over the salt when borne by said conveyor,substantially as described. I

34. The method herein described of precipitating a salt from a solutionwhich consists in causing the solution to flow countercurrent in loopform, the branches of the circuit in heat-exchanging relation one toanother, cooling the flowing stream throu h-- out a portion of the loop,and collecting precipitate from the flowing stream throughout the regionof cooling and beyond.

In testimony whereof we have hereunto set our hands.

HENRY S. MARSH. RALF S. COOHRAN.

Witnesses:

S. M. WATT, ETHEL JONES.

